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            <h2 class="title" style="clear: both"><a id="env_naming"></a>File naming</h2>
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        <dl>
          <dt>
            <span class="sect2">
              <a href="env_naming.html#id1605342">Specifying file naming to Berkeley DB</a>
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          <dt>
            <span class="sect2">
              <a href="env_naming.html#id1605560">Filename resolution in Berkeley DB</a>
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            <span class="sect2">
              <a href="env_naming.html#id1605734">Examples</a>
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      <p>One of the most important tasks of the database environment is to
structure file naming within Berkeley DB.  Cooperating applications (or
multiple invocations of the same application) must agree on the location
of the database environment, log files and other files used by the Berkeley DB
subsystems, and, of course, the database files.  Although it is possible
to specify full pathnames to all Berkeley DB methods, this is cumbersome and
requires applications be recompiled when database files are moved.</p>
      <p>Applications are normally expected to specify a single directory home
for the database environment.  This can be done easily in the call to
<a href="../api_reference/C/envopen.html" class="olink">DB_ENV-&gt;open()</a> by specifying a value for the <span class="bold"><strong>db_home</strong></span>
argument.  There are more complex configurations in which it may be
desirable to override <span class="bold"><strong>db_home</strong></span> or provide supplementary path
information.</p>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="id1605342"></a>Specifying file naming to Berkeley DB</h3>
            </div>
          </div>
        </div>
        <p>The following list describes the possible ways in which file naming
information may be specified to the Berkeley DB library.  The specific
circumstances and order in which these ways are applied are described
in a subsequent paragraph.</p>
        <div class="variablelist">
          <dl>
            <dt>
              <span class="term">db_home</span>
            </dt>
            <dd>If the <span class="bold"><strong>db_home</strong></span> argument to <a href="../api_reference/C/envopen.html" class="olink">DB_ENV-&gt;open()</a> is non-NULL,
its value may be used as the database home, and files named relative to
its path.</dd>
            <dt>
              <span class="term">DB_HOME</span>
            </dt>
            <dd>
              <p>If the DB_HOME environment variable is set when <a href="../api_reference/C/envopen.html" class="olink">DB_ENV-&gt;open()</a> is
called, its value may be used as the database home, and files named
relative to its path.</p>
              <p>The DB_HOME environment variable is intended to permit users and system
administrators to override application and installation defaults.  For
example::</p>
              <pre class="programlisting">env DB_HOME=/database/my_home application</pre>
              <p>Application writers are encouraged to support the <span class="bold"><strong>-h</strong></span> option
found in the supporting Berkeley DB utilities to let users specify a database
home.</p>
            </dd>
            <dt>
              <span class="term"><a href="../api_reference/C/env.html" class="olink">DB_ENV</a> methods</span>
            </dt>
            <dd> There are three <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> methods that affect file naming.  The
<a href="../api_reference/C/envset_data_dir.html" class="olink">DB_ENV-&gt;set_data_dir()</a> method specifies a directory to search for database
files.  The <a href="../api_reference/C/envset_lg_dir.html" class="olink">DB_ENV-&gt;set_lg_dir()</a> method specifies a directory in which to
create logging files.  The <a href="../api_reference/C/envset_tmp_dir.html" class="olink">DB_ENV-&gt;set_tmp_dir()</a> method specifies a
directory in which to create backing temporary files.  These methods
are intended to permit applications to customize a file location for a
database.  For example, an application writer can place data files and
log files in different directories or instantiate a new log directory
each time the application runs.</dd>
            <dt>
              <span class="term">
                <a class="link" href="env_db_config.html" title="DB_CONFIG configuration file">DB_CONFIG</a>
              </span>
            </dt>
            <dd>The same information specified to the <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> 
        methods may also be specified using the <a class="link" href="env_db_config.html" title="DB_CONFIG configuration file">DB_CONFIG</a> 
        configuration file.</dd>
          </dl>
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      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="id1605560"></a>Filename resolution in Berkeley DB</h3>
            </div>
          </div>
        </div>
        <p>The following list describes the specific circumstances and order in
which the different ways of specifying file naming information are
applied.  Berkeley DB filename processing proceeds sequentially through the
following steps:</p>
        <div class="variablelist">
          <dl>
            <dt>
              <span class="term">absolute pathnames</span>
            </dt>
            <dd>If the filename specified to a Berkeley DB function is an <span class="emphasis"><em>absolute
pathname</em></span>, that filename is used without modification by Berkeley DB.
<p>On UNIX systems, an absolute pathname is defined as any pathname that
begins with a leading slash (<span class="bold"><strong>/</strong></span>).</p><p>On Windows systems, an absolute pathname is any pathname that begins with
a leading slash or leading backslash (<span class="bold"><strong>\</strong></span>); or any
pathname beginning with a single alphabetic character, a colon and a
leading slash or backslash (for example, <code class="filename">C:/tmp</code>).</p></dd>
            <dt>
              <span class="term"><a href="../api_reference/C/env.html" class="olink">DB_ENV</a> methods, DB_CONFIG</span>
            </dt>
            <dd>If a relevant configuration string (for example, set_data_dir), is
specified either by calling a <a href="../api_reference/C/env.html" class="olink">DB_ENV</a> method or as a line in the
<a class="link" href="env_db_config.html" title="DB_CONFIG configuration file">DB_CONFIG</a> configuration file, the value is prepended to the
filename.  If the resulting filename is an absolute pathname, the
filename is used without further modification by Berkeley DB.</dd>
            <dt>
              <span class="term">db_home</span>
            </dt>
            <dd>If the application specified a non-NULL <span class="bold"><strong>db_home</strong></span> argument to
<a href="../api_reference/C/envopen.html" class="olink">DB_ENV-&gt;open()</a>, its value is prepended to the filename.  If the
resulting filename is an absolute pathname, the filename is used without
further modification by Berkeley DB.</dd>
            <dt>
              <span class="term">DB_HOME</span>
            </dt>
            <dd>If the <span class="bold"><strong>db_home</strong></span> argument is NULL, the DB_HOME environment
variable was set, and the application has set the appropriate
<a href="../api_reference/C/envopen.html#envopen_DB_USE_ENVIRON" class="olink">DB_USE_ENVIRON</a> or <a href="../api_reference/C/envopen.html#envopen_DB_USE_ENVIRON_ROOT" class="olink">DB_USE_ENVIRON_ROOT</a> flags, its value
is prepended to the filename.  If the resulting filename is an absolute
pathname, the filename is used without further modification by Berkeley DB.</dd>
            <dt>
              <span class="term">default</span>
            </dt>
            <dd>Finally, all filenames are interpreted relative to the current working
directory of the process.</dd>
          </dl>
        </div>
        <p>The common model for a Berkeley DB environment is one in which only the DB_HOME
environment variable, or the <span class="bold"><strong>db_home</strong></span> argument is specified.  In
this case, all data filenames are relative to that directory, and all
files created by the Berkeley DB subsystems will be created in that directory.</p>
        <p>The more complex model for a transaction environment might be one in
which a database home is specified, using either the DB_HOME environment
variable or the <span class="bold"><strong>db_home</strong></span> argument to <a href="../api_reference/C/envopen.html" class="olink">DB_ENV-&gt;open()</a>; and then
the data directory and logging directory are set to the relative
pathnames of directories underneath the environment home.</p>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="id1605734"></a>Examples</h3>
            </div>
          </div>
        </div>
        <p>Store all files in the directory <code class="filename">/a/database</code>:</p>
        <pre class="programlisting">dbenv-&gt;open(dbenv, "/a/database", flags, mode);</pre>
        <p>Create temporary backing files in <code class="filename">/b/temporary</code>, and all other files
in <code class="filename">/a/database</code>:</p>
        <pre class="programlisting">dbenv-&gt;set_tmp_dir(dbenv, "/b/temporary");
dbenv-&gt;open(dbenv, "/a/database", flags, mode);</pre>
        <p>Store data files in <code class="filename">/a/database/datadir</code>, log files in
<code class="filename">/a/database/logdir</code>, and all other files in the directory
<code class="filename">/a/database</code>:</p>
        <pre class="programlisting">dbenv-&gt;set_lg_dir(dbenv, "logdir");
dbenv-&gt;set_data_dir(dbenv, "datadir");
dbenv-&gt;open(dbenv, "/a/database", flags, mode);</pre>
        <p>Store data files in <code class="filename">/a/database/data1</code> and <code class="filename">/b/data2</code>, and
all other files in the directory <code class="filename">/a/database</code>.  Any data files
that are created will be created in <code class="filename">/b/data2</code>, because it is
the first data file directory specified:</p>
        <pre class="programlisting">dbenv-&gt;set_data_dir(dbenv, "/b/data2");
dbenv-&gt;set_data_dir(dbenv, "data1");
dbenv-&gt;open(dbenv, "/a/database", flags, mode);</pre>
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